Originally posted by squala
Isn't it that if they can prove the correct air-fuel mixture through reliable measures, then the NOx issue is settled?
for starters, the ECU is already doing that! that's why you have all those sensors (lambda/o2, air mass, etc)!

now, what this devices does is to put in additional air after the ECU has calculated the optimal air-fuel mixture. this would result in a lean mixture.

as i've said before, a lean mixture would slightly improve HC & CO emmission and fuel consumption - BUT the downside of it is that large amount of NOx will not be burned up by the catalyst.

that's because the catalytic converter operates at around 1 to 0.9 lambda (or 15:1 air-fuel mix). any changes in the mixture (like what the device is doing) would result in non-optimal performance of the catalytic converter.

now, what I don't get is how on earth will the said device "measure" the air-fuel mixture and on how it will interact with the ECU.